The present invention relates to linerless closures for containers including, but not limited to, carbonated beverage containers. More particularly, the invention relates to such closures that are formed of a synthetic plastics material and, preferably, in one piece.
U.S. Pat. No. 5,423,444 discloses a plastic closure for a container having an externally screw threaded neck, the closure including a top portion and an internally threaded skirt. The closure has an annular sealing rib which projects downwardly from the underside of the top portion. The rib includes a first, substantially cylindrical portion contiguous with the underside of the top portion and lying adjacent to or abutting with the skirt, and a second, frusto-conical, portion contiguous with the end of the first portion distal to the underside of the top portion and extending radially inwardly to a circular free edge. During threaded attachment of the closure with the neck, the second, frusto-conical, portion will be engaged by a free end of the neck and folded back against the first, substantially cylindrical portion of the rib to form a gas tight seal between the neck of the container and the closure.
U.S. Pat. No. 5,609,263 discloses a variant of the above closure in which there is at the free end of the second portion of the rib a thick seal ring of substantially circular cross-sectional shape. The rib and the seal ring are dimensioned to engage the free end of the neck when the closure is threaded onto the neck such that when the neck is fully screwed into the closure its free end crushes the seal ring directly against the inside surface of the top portion of the closure.
The present invention is directed to two arrangements of closure that improve the sealing ability of closures of the type identified in the abovementioned prior art.
The present invention relates to a closure suitable for mounting onto a container having an opening defined by an end portion of the container, the closure being moulded from a synthetic plastics material and including a top portion and a skirt portion depending from the top portion, an annular sealing rib projecting downwardly from an underside of the top portion, the rib including a first portion which is contiguous with the top portion and having an inner surface, which inner surface lies radially inwardly of the skirt portion, and a second, frusto-conical, portion contiguous with the first portion and separated from the top portion by the inner surface of the first portion, the second portion extending radially inwardly to terminate in a circular edge, the first portion having an internal diameter relative to the external diameter of the end portion of the container such that during attachment of the closure with the end portion of the container, the second frusto-conical portion of the sealing rib will be engaged by a free end of said end portion of the container and folded back at least adjacent the inner surface of the first portion of the rib, the closure being characterised in that the first portion of the rib increases in thickness as it extends away from the top portion of the closure.
In a second aspect, the present invention relates to a closure suitable for mounting onto a container having an opening defined by an end portion of the container the closure being moulded from a synthetic plastics material and including a top portion and a skirt portion depending front the top portion, an annular sealing rib projecting downwardly from an underside of the top portion, the rib including a first portion which is contiguous with the top portion and having an inner surface, which inner surface lies radially inwardly of the skirt portion, and a second, frusto-conical, portion contiguous with the first portion and separated from the top portion by the inner surface of the first portion, the second portion extending radially inwardly to terminate in a circular edge, the closure being characterised in that the sealing rib has a third portion connected to the second portion at or adjacent the circular edge and extending generally in a direction away from the top portion, the third portion being substantially no thicker than the second portion and having a length longer than its thickness, the first portion having an internal diameter relative to the external diameter of the end portion of the container such that during attachment of the closure with the end portion of the container, the second frusto-conical portion of the sealing rib will be engaged by a free end of said end portion of the container and folded back at least adjacent the inner surface of the first portion of the rib, and with the third portion of the rib positioned between the neck of the container and the top portion of the closure.
The closures are preferably provided with a screw thread on the inside surface of the skirt portion adapted to engage with a corresponding thread on an external surface of the end portion of the container. It is, however, possible for the container and the closure to be formed with other complementary attachment means. Such an arrangement could, for instance, comprise snap-on attachment means having a rib on the inside surface of the closure and a corresponding groove on the outside surface of the end portion of the container.
The first portion of the rib is preferably formed radially inwardly of the skirt with an annular space therebetween. It is, however, possible in other embodiments to form the first portion of the rib in abutment with the skirt in the sense that they are continuous. In one embodiment of the above aspects of the invention, the first portion of the rib is observed as a thickening of the skirt portion so that the root of the second portion of the rib is moved inwardly of the part of the skirt portion carrying the screw thread or other attachment means.
In each aspect, the first portion serves to form an abutment towards which the second portion is folded during attachment of the closure with the end portion of a container. Preferably, the second portion will be folded back against the first portion such that it bears against the inner surface of the first portion. This will cause the second portion to bear more strongly against the outside surface of the end portion of the container and so form a better seal with the end portion.
The first aspect of the present invention is directed to the first portion of the rib having a thickness that increases in a direction away from the top portion of the closure. This thickening of the first portion will increase the force of the pressure of the rib against the outside surface of the end portion of the closure. The thickness of the first portion preferably increases at a uniform rate along the length of the first portion however it could do so in a non-uniform manner. The increase in the thickness of the first portion means that the inside and outside surfaces of the first portion will not necessarily be exactly cylindrical. They my respectively taper slightly inwardly and outwardly relative to the axis of the closure in a direction away from the top portion of the closure.
In the second aspect of the present invention, the rib includes a third portion. This third portion is preferably contiguous with the free edge of the second portion, though it may be spaced slightly radially outwardly front it. The third portion projects generally away front the top of the closure. It may join the second portion in an angular disjunction or it may join it in a smooth angular transition from the generally radially inward direction of the second portion to a generally axial direction.
It is of the essence of this second aspect of the present invention that the third portion of the rib be substantially no thicker than the second portion and also be relatively longer in relation to its thickness. It has been found that the sealing qualities of the closure are best improved by providing a thin extension to the second portion of the rib that will wrap around the free end of the end portion of the container front a position on a cylindrical outer surface of the end portion at least to the apex of the free end of the end portion. It has also been found that this construction also reduces the torque needed to unscrew a closure from a corresponding container to which it has been attached.
The closures according to the present invention may be made of any suitable synthetic plastics material, however it is preferred to form them from a suitable grade of polyethylene or polypropylene. It is also preferred to form the closure in one piece by injection or rotary moulding. The closures could, however, be formed in two parts with the sealing rib formed separately from the top portion and the skirt portion.
It will be apparent to persons skilled in the art that numerous modifications may be made to the closures described in this specification without departing from the scope of the invention as earlier defined. The closure may, for instance, be provided with a tamper evident band, for example a band such as is described in Australian patent specifications 668197 and 683598, the contents whereof are incorporated herein by reference.
Where the closure has a screw thread on the inner surface of the skirt, the thread can be continuous or formed of a series of thread segments. If formed front a series of thread segments, the thread segments can be arranged, starting from a first thread segment distal to the top, along a helical thread locus, as is described in Australian patent specification 668197. Each of the thread segments except the first can be formed with two substantially planar end surfaces that are inclined to the axis of the closure and face away from the top of the closure, that is they face in the direction that a mould core used to mould the closure was withdrawn. In this specification, the term xe2x80x9csubstantially planar surfacexe2x80x9d is used to describe a surface that is nearly actually planar or that is curved provided that it all faces in the defined direction. The first of the thread segments is preferably pointed at its end distal to its one adjacent thread segment to assist in sating the thread on the closure with a complementary thread on the neck of a container.
The substantially planar ends of the thread segments can also be inclined to a notional radial plane of the closure extending from the longitudinal axis of the closure to the end of the respective thread segment such that the ends are inclined to the cylindrical skirt by an angle that is less than the angle that the respective notional plane makes with that skirt.
To assist in the venting of gas that may be present in the container, the spaces between the thread segments in adjacent turns of the thread can be aligned. A groove may also be provided on the inside surface of the skirt of the closure extending longitudinally thereof through the aligned spaces.
There also can be at the line of meeting of the first and second portions of the sealing rib, a weakened zone or annular region of weakness to assist even deformation of the second portion relative to the first as the closure is applied to a container as is described in Australian patent specification 637706, the contents whereof are incorporated herein by reference.
The underside of the top portion of the closure can also have a continuous or segmented annular ridge radially inside of the sealing rib. The upper surface of the second portion of the rib may also be formed with an engagement means comprising a segmented or continuous annular ridge as is described in Australian patent specification 74544/94, the contents whereof are incorporated herein by preference. On attachment of the closure with the neck of a container, the engagement means engage with the underside of the top portion.
In accordance with the above, the closure can have a taper evident band adapted to provide an indication of removal or attempted removal of the closure from a container. The tamper evident band can extend from the skirt portion by connection through a plurality of frangible bridges.
The band can also comprise a generally cylindrical body portion and a segmented rib extending inwardly of the body portion and adapted to provide a lip having an inner free edge to engage under a retaining flange extending outwardly from the end portion of the container, characterised in that the combined length of the segmented ribs is equal to at least 50% of the internal circumference of the band and the segmented ribs are separated from each other by a gap, the rib segments each having an upper surface facing generally towards the top portion of the closure and an underside facing generally away from the top portion, the inner surface of the band having a plurality of radially inward projections extending from above the free edge of the band and not extending beyond the inner free edge of the lip.
The band can also comprise a generally cylindrical body portion and a segmented rib extending inwardly of the body portion and adapted to provide a lip having an inner free edge to engage under a retaining flange extending outwardly from the end portion of the container, the rib segments each having an upper surface facing generally towards the top portion of the closure and an underside facing generally away from the top portion, characterised in that the upper surface of each rib comprises a first surface contiguous with the body portion of the band, which surface slopes inwardly and downwardly away from the top portion, and a second surface which extends radially inwardly from the inner terminus of the first surface and has a slope angle substantially normal to the skirt portion of the closure.